Many communication networks that provide high bit-rate transport over a shared medium are characterized by a non-continuous or burst data transmission. A typical PON includes a plurality of optical network units (ONUs) connected to an optical line terminal (OLT) via a passive optical splitter. Traffic data transmission is performed over two optical wavelengths, one for the downstream direction and another for the upstream direction. Thus, downstream transmission from the OLT is broadcast to all ONUs, where each ONU filters its respective data according to, for example, pre-assigned labels. In the upstream direction, an ONU transmits data to the OLT during different time slots allocated by the OLT. Transmission from an ONU to the OLT is in the form of a burst.
An OLT includes an optical transceiver that receives burst data and transmits continuous data. A received burst data signal is preceded by a low logic value (‘0’) signal transmitted on the optical line. This is performed mainly to enable the recovery of the received signals and without losing any data bits, as required, for example, by the Gigabit PON (GPON) communication standard.
FIG. 1 shows a schematic diagram of an OLT 100 that includes an optical transceiver 110 and a medium access control (MAC) module 120. A transmitter (not shown) of the optical transceiver 110 generates and transmits optical signals respective of the input data signals. The optical transceiver 110 also includes a burst mode receiver (not shown) that receives burst signals sent from the ONUs. The optical transceiver 110 generates electric digital signals respective of the received burst data signals. The MAC module 120 processes digital electric signals provided by the optical transceiver 110.
The MAC module 120 is a logic component implemented in en integrated circuit (IC). The MAC module 120 and optical transceiver 110 operate at different direct current (DC) levels. Typically, the DC level of the MAC module 120 is significantly lower than the DC level of the optical transceiver 110, in particular, when the size of the IC including the MAC module 110 is designed to support advanced semiconductor fabrication techniques.
The data burst signals output by the optical transceiver 110 are offset by a certain biased DC level, which is typically the operation voltage of the transceiver. However, as the DC level of the MAC module 120 is lower than that of the transceiver 110, the burst signal may not be properly received at the MAC module 120.
Therefore, it would be advantageous to provide a solution for interfacing between the MAC module and the optical transceiver in order to properly receive data burst signals.